Transition structure for coupling first and second transmission lines through a multi-layer structure and including a cavity corresponding to the second transmission line

A transition structure for millimeter wave is provided. The transition structure includes a first layer signal element coupled to an end of a first transmission line and a plurality of first layer ground elements surrounding the end of the first transmission line equidistantly from the end of the first transmission line and disposed along two opposite sides of a strip body of the first transmission line equidistantly from the strip body of the first transmission line. The transition structure further includes an intermediate layer signal element coupled to the first layer signal element and a plurality of intermediate layer ground elements surrounding the intermediate layer signal element quasi-coaxially. A multilayer transition structure including a multilayer structure and the transition structure is also provided. Therefore, the problem of operating frequency caused by the thickness of the multilayer structure can be overcome, thereby increasing the resonance frequency of the multilayer structure.